The beta2 integrin CD11b/CD18, the most abundant leukocyte integrin, is normally kept in an inactive (low affinity) state on circulating neutrophils and monocytes. Exposure of these cells to agonists, such as chemokines, elicits tightly-regulated intracellular interactions with the integrin's cytoplasmic tails that switch the conformation of the integrin ectodomain into a high affinity (ligand-competent) state, a process known as inside-out activation. Active integrins allow phagocytes to leave the blood circulation into tissues, where they participate in immune clearance. When integrin regulation fails, phagocytes become too sticky, leading to subversive inflammation. Despite extensive studies, a mechanistic understanding of how the integrin is kept in a default inactive state in quiescent phagocytes is incompletely understood, despite the key role of this mechanism in ensuring host survival. In addition, the atomic structure of the full-length ectodomain in the high affinity stat is still unknown, despite the importance of defining this structure in testing current models of integrin activation and for structure-guided design and optimization of antagonists. And previous attempts to block the proinflammatory functions CD11b/CD18 lacked adequate power to demonstrate efficacy in controlled clinical settings and often targeted simultaneously the three other beta2 integrins as well, confounding interpretation of outcomes. The present application seeks to unravel the atomic structure of high affinity CD11b/CD18 ectodomain, determine the role of a novel atypical phosphatase in maintaining the default inactive state in leukocytes and assess the impact of stabilizing this inactive state with a primate-specific monoclonal antibody (that possesses a unique mechanism of action), in protection of the kidney from Delayed Graft Function, an increasingly common clinical problem with no effective therapy. Biochemical, immunochemical, genetic and structural approaches and animal models will be utilized by a multidisciplinary group of investigators to achieve these goals. PUBLIC HEALTH RELEVANCE: The role of integrin CD11b/CD18 in phagocyte-mediated ischemic or immune kidney injury is established experimentally. However, how this pro-inflammatory integrin is maintained in its inactive state in resting phagocytes to prevent injury, the atomic structure it assumes in the proinflammatory state, and if therapies can be developed and successfully applied to block transition to this potentially harmful state are unanswered questions. These will be directly addressed in the proposed biochemical, crystallographic and interventional/therapeutic studies.